This invention relates to a timed battery charger and particularly relates to a timer control system which operates in duty cycle modes for controlling the charging of a battery.
In known systems for charging a nickel cadmium battery, current at a first level is supplied continuously to the battery for a prescribed period to effect a full charge of the battery. Thereafter, current at a second or trickle level, lower than the first level, is supplied to the battery for a prescribed period or until the battery is removed or disconnected from the charging facility. In other systems, an additional precharge level of current, which typically falls between the above-mentioned first and second rates, is supplied to the battery to raise the voltage level thereof in preparation for acceptance of the charging current at the first level.
In a few instances, some of the various phases of charging operations at different rates of charging current are further controlled by operating at selected duty cycles. This selectively controls the amount of current supplied at a particular level of current for the above-described multiple level systems.
In systems of the types described above, complex and expensive circuit designs are necessitated to provide the current supply sources for supplying the various rates required to process through a complete charging cycle. Further, multiple interfacing circuits are required between timer control facilities of such chargers, duty-cycle control facilities and the several current supply sources necessary in providing charging current at the plurality of rates.
Systems which include some of the above-noted features are described in U.S. Pat. No. 4,394,611 which issued on Jul. 19, 1983, U.S. Pat. No. 4,554,500 which issued on Nov. 9, 1985 and U.S. Pat. No. 4,670,703 which issued on Jun. 2, 1987.
Each of the systems shown n the above-noted patents utilizes the multiple-level charging current approach. This arrangement requires additional circuit facilities to provide the charging current at different rates with complex and expanded interfacing circuits necessary for the timing and duty-cycle control where utilized. With complex and expanded circuits required, the cost of such charging systems is high and the operational energy requirement is high and costly because of the number and type of components used in such systems.
Therefore, there is a need for a charger which is not complex in construction and is inexpensive to operate but which will provide the advantages obtainable when operating in a timed, duty-cycle manner.